Small improvements

app/src/main/java/eu/faircode/email/Core.java

@@ -120,7 +120,8 @@ class Core {
     private static final long YIELD_DURATION = 200L; // milliseconds
     private static final long MIN_HIDE = 60 * 1000L; // milliseconds
 
-    private static final ExecutorService executor = Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
+    private static final ExecutorService executor =
+            Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
 
     static void processOperations(
             Context context,

app/src/main/java/eu/faircode/email/DB.java

@@ -97,7 +97,7 @@ public abstract class DB extends RoomDatabase {
     public abstract DaoLog log();
 
     private static DB sInstance;
-    private static ExecutorService executor = Executors.newFixedThreadPool(
+    private static final ExecutorService executor = Executors.newFixedThreadPool(
             Runtime.getRuntime().availableProcessors(), Helper.backgroundThreadFactory);
 
     private static final String DB_NAME = "fairemail";

app/src/main/java/eu/faircode/email/EmailProvider.java

@@ -377,7 +377,8 @@ public class EmailProvider {
         return provider;
     }
 
-    private static final ExecutorService executor = Executors.newCachedThreadPool();
+    private static final ExecutorService executor =
+            Executors.newCachedThreadPool(Helper.backgroundThreadFactory);
 
     private static class Server {
         String host;

app/src/main/java/eu/faircode/email/EntityLog.java

@@ -48,7 +48,8 @@ public class EntityLog {
     @NonNull
     public String data;
 
-    private static ExecutorService executor = Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
+    private static final ExecutorService executor =
+            Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
 
     static void log(Context context, String data) {
         Log.i(data);

app/src/main/java/eu/faircode/email/Helper.java

@@ -141,7 +141,8 @@ public class Helper {
         }
     };
 
-    private final static ExecutorService executor = Executors.newSingleThreadExecutor();
+    private static final ExecutorService executor =
+            Executors.newSingleThreadExecutor(backgroundThreadFactory);
 
     // Features
 

app/src/main/java/eu/faircode/email/HtmlHelper.java

@@ -85,7 +85,8 @@ public class HtmlHelper {
     private static final List<String> tails = Collections.unmodifiableList(Arrays.asList(
             "h1", "h2", "h3", "h4", "h5", "h6", "p", "ol", "ul", "li"));
 
-    private static final ExecutorService executor = Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
+    private static final ExecutorService executor =
+            Executors.newSingleThreadExecutor(Helper.backgroundThreadFactory);
 
     static String sanitize(Context context, String html, boolean show_images) {
         Document parsed = Jsoup.parse(html);